In cellular telephones, radio frequency (R.F) power amplifiers (PA) are built using a semiconductor device (e.g., silicon or GaAs) that has a low output impedance (e.g., less two ohms). 1 0 This impedance needs to be transformed to a higher impedance value (e.g., fifty ohms) to connect to filters, switches, diplexers and antennas in the rest of the radio. This impedance transformation network is typically referred to as the “output match.”
In addition to transforming a two-ohm impedance to fifty ohms, the output match is typically tuned at the harmonic frequencies to increase efficiency and battery life (e.g., talk time) of the cellular telephone. These harmonic frequencies extend up to 6 GHz. At these frequencies, the distance between the capacitors and other passive components used to construct the output match is critical, for example a distance of 0.001″ is significant. For example, a vendor may specify distances of 0.062″ and 0.416″ in one one-thousandth of an inch of precision between the capacitors and other passive components of the output matching network.
The harmonic frequencies present a second problem. The capacitors have parasitic values that become significant at the harmonic frequencies. Since the parasitic values differ from one manufacturer to another, changing vendors for the same value component will yield different results.
In producing high volumes (e.g., 30,000,000 per year) these dependencies on a single vendor and tolerances of 0.001″ are costly to manage. Therefore, there is a need for an improved technique for providing an impedance matching network.